如何在没有任何数字丢失的情况下获得具有连续增加数字的列？

Question

可能重复:
如何在PostgreSQL查询中显示行号？
在Postgresql PostgreSQL中重新排序带有标识符的列使用带子
选择的更新重新排序

我只是问在PostgreSQL中是否存在这样的可能性:如果我有5行并且在一列中有数字1, 2, 3, 4, 5并且在那些列中不是主键如果我删除说tird行postgreSQL重新枚举这个列所以我可以1, 2, 3, 4代替1, 2, 4, 5？

Answer 1

改编自先前的答案。当应用程序想要变量的制表顺序（读取：EAV模型中的记录）时，这种情况经常发生，这也可能是备用键（的一部分）。

• 该priority字段需要保持连续。[这是制表顺序 ]
• 在INSERT上：所有优先级> =新记录的记录的优先级应递增
• 同样：在DELETE->递减
• 如果记录的优先级通过UPDATE更改，则旧优先级值和新优先级值之间的记录的优先级应上移或下移。
• 为了避免递归触发调用：
  • 基于触发器的更新会将flipflag其触摸的所有记录翻转。
  • 他们进行测试old.flipflag=new.flipflag以检测实际更新。（不是由触发器引起的）

        -- Make some data
DROP SCHEMA tmp CASCADE;
CREATE SCHEMA tmp ;
SET search_path=tmp;

CREATE TABLE fruits
        ( id INTEGER NOT NULL PRIMARY KEY
        , priority INTEGER NOT NULL
        , flipflag boolean NOT NULL default false
        , zname varchar NOT NULL
        , CONSTRAINT unique_priority UNIQUE (priority) DEFERRABLE INITIALLY DEFERRED
        );
INSERT INTO fruits(id,zname,priority) VALUES
 (1  , 'Pear' ,4)
,(2  , 'Apple' ,2)
,(3  , 'Orange' ,1)
,(4  , 'Banana' ,3)
,(5  , 'Peach' ,5)
        ;

        -- Trigger functions for Insert/update/delete
CREATE function shift_priority()
RETURNS TRIGGER AS $body$

BEGIN
        UPDATE fruits fr
        SET priority = priority +1
        , flipflag = NOT flipflag       -- alternating bit protocol ;-)
        WHERE NEW.priority < OLD.priority
        AND OLD.flipflag = NEW.flipflag -- redundant condition
        AND fr.priority >= NEW.priority
        AND fr.priority < OLD.priority
        AND fr.id <> NEW.id             -- exlude the initiating row
                ;
        UPDATE fruits fr
        SET priority = priority -1
        , flipflag = NOT flipflag
        WHERE NEW.priority > OLD.priority
        AND OLD.flipflag = NEW.flipflag
        AND fr.priority <= NEW.priority
        AND fr.priority > OLD.priority
        AND fr.id <> NEW.id
        ;
        RETURN NEW;
END;

$body$
language plpgsql;

CREATE function shift_down_priority()
RETURNS TRIGGER AS $body$

BEGIN

        UPDATE fruits fr
        SET priority = priority -1
        , flipflag = NOT flipflag       -- alternating bit protocol ;-)
        WHERE fr.priority > OLD.priority
                ;
        RETURN NEW;
END;

$body$
language plpgsql;

CREATE function shift_up_priority()
RETURNS TRIGGER AS $body$

BEGIN
        UPDATE fruits fr
        SET priority = priority +1
        , flipflag = NOT flipflag       -- alternating bit protocol ;-)
        WHERE fr.priority >= NEW.priority
                ;
        RETURN NEW;
END;

$body$
language plpgsql;

        -- Triggers for Insert/Update/Delete
CREATE TRIGGER shift_priority_u
        AFTER UPDATE OF priority ON fruits
        FOR EACH ROW
        WHEN (OLD.flipflag = NEW.flipflag AND OLD.priority <> NEW.priority)
        EXECUTE PROCEDURE shift_priority()
        ;
CREATE TRIGGER shift_priority_d
        AFTER DELETE ON fruits
        FOR EACH ROW
        EXECUTE PROCEDURE shift_down_priority()
        ;
CREATE TRIGGER shift_priority_i
        BEFORE INSERT ON fruits
        FOR EACH ROW
        EXECUTE PROCEDURE shift_up_priority()
        ;

        -- Do some I/U/D operations
\echo Pears are Okay
UPDATE fruits
SET priority = 1
WHERE id=1; -- 1,4

SELECT * FROM fruits ORDER BY priority;

\echo dont want bananas
DELETE FROM fruits WHERE id = 4;
SELECT * FROM fruits ORDER BY priority;

\echo  We want Kiwis
INSERT INTO fruits(id,zname,priority) VALUES (4  , 'Kiwi' ,3) ;
SELECT * FROM fruits ORDER BY priority;

结果：

Pears are Okay
UPDATE 1
 id | priority | flipflag | zname  
----+----------+----------+--------
  1 |        1 | f        | Pear
  3 |        2 | t        | Orange
  2 |        3 | t        | Apple
  4 |        4 | t        | Banana
  5 |        5 | f        | Peach
(5 rows)

dont want bananas
DELETE 1
 id | priority | flipflag | zname  
----+----------+----------+--------
  1 |        1 | f        | Pear
  3 |        2 | t        | Orange
  2 |        3 | t        | Apple
  5 |        4 | t        | Peach
(4 rows)

We want Kiwis
INSERT 0 1
 id | priority | flipflag | zname  
----+----------+----------+--------
  1 |        1 | f        | Pear
  3 |        2 | t        | Orange
  4 |        3 | f        | Kiwi
  2 |        4 | f        | Apple
  5 |        5 | f        | Peach
(5 rows)